UxAu100−x thin films (x = 0 to 100 at.%) have been prepared by sputter deposition and studied in situ by use of x-ray photoemission spectroscopy and ultraviolet spectroscopy. The valence band displays a two-peak structure near the Fermi level (EF ), one (peak α) pointing at EF , characteristic of itinerant 5f states, and one (peak β) at ∼0.7 eV, which is representative of localized 5f states. The presence of the peak α at all the composition of the series (x = 0 to 100 at.%) shows that 5f states are never purely localized. The evolution of the full width at half maximum of the 5f line displays three main domains of composition where the interaction evolves from a (5f , ligand states) (x < 25 at.%) hybrid band to a pure 5f band (x > 50 at.%). In an intermediate domain (30–50 at.%), the Au 5d6s conduction band narrows and shifts to higher binding energy at the extent of the interaction with U 5f states. A correlation of the valence band spectra is made with the U 4f core-level peak where the shape evolves from a three-peak structure (x < 10 at.%), characteristic of a mixed valence state, to a single-peak structure (x _ 30 at.%). Relativistic electronic structure theory based on the local density approximation plus exact diagonalization of a multiorbital Anderson impurity model explains well the valence photoemission features. The essential role of hybridization in the U-based systems is emphasized.